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Nanotech ’tissue’ loves oil spills, hates water

By Mason Inman

This tangled mix of manganese oxide repels water – but it will absorb 20 times its own weight in engine oil

(Image: Nature)

A material with remarkable oil-absorbing properties has been developed by US researchers. It could help develop high-tech “towels” able to soak up oil spills at sea faster, protecting wildlife and human health.

Clean-up methods have improved in recent years, but separating oil from thousands of gallons of water is still difficult and perhaps the biggest barrier to faster clean ups.

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The new water-repellent material is based on manganese oxide nanowires and could provide a blueprint for a new generation of oil-spill cleaners. It is able to absorb up to 20 times its own weight in oil, without sucking up a drop of water.

Oil guzzler

Researchers led by Francesco Stellacci at the Massachusetts Institute of Technology in Cambridge, US, made membranes of tangled manganese oxide nanowires around 50 micrometres thick – about a quarter of the thickness of normal office paper.

The tiny wires are first suspended in liquid, before being strained out into flat sheets. “It’s very similar to the process that makes paper,” Stellacci says.

The manganese oxide nanowires are normally very attractive to water. However, adding a silicon coating switches the material to being strongly water repellent. It also becomes able to guzzle oil. Tests showed the material can suck up 20 times its weight in motor oil, and 10 times its weight in gasoline.

The new material is much more selective than other similar materials, such as those made of polymer or glass fibres, tests showed. Those materials all absorb some water as well as oil.

Heat proof

“Our material can be left in water a month or two, and when you take it out it’s still dry,” Stellacci says. “But if that water contains some hydrophobic [oily] contaminants they will get absorbed.”

The membranes are tough, too, and can withstand being heated to evaporate off any oils. High temperatures remove the silicon coating, but once a new one is applied, the membrane is ready to use again, the researchers showed.

The membrane has “extraordinary selectivity and capacity for the separation of oil from water,” says Joerg Lahann of the University of Michigan in Ann Arbor, US.

But Lahann points out that manganese oxide may not be the best material for real-world applications because it could be toxic. He says, though, that the new material “clearly provides a blueprint that can guide the design of future nanomaterials for environmental applications.”